Bar codes giving product information such as date of production, names of the producer and the distributor, term of validity, etc. have heretofore been widely used for a variety of kinds of products. Here, the bar codes are such that the coded information is read through a reader. Therefore, the surface where the bar codes are printed must be flat encountering limitations in the field of packing materials such as bottles and caps. There, further, remains a problem of limited amount of information that can be coded.
Recently, therefore, a technology for giving information by using an IC tag has been utilized. The IC tag is also called RFID (Radio Frequency Identification) and is a micro-communication terminal formed in the shape of a tag (label) obtained by burying an IC chip storing predetermined information together with a radio antenna in a dielectric material such as resin or glass. The IC tag is used for reading product information stored in the IC chip via radio communication and offers such an advantage that a memory in the IC chip is capable of storing data of, for example, several hundreds of bytes and, therefore, can store a lot of product information. Besides, the IC tag can be used for reading the recorded information in a non-contacting manner, is free of problem of wear caused by contact and, further, offers such advantages that it can be worked in a shape that meets the form of the product and in a small size with a decreased thickness.
For example, a patent document 1 discloses a cap in which an IC tag is buried in a top plate.